Assus, ancient Greek city of the Troad, located on the coast of what is now northwestern Turkey, with the island of Lesbos lying about 7 miles (11 km) offshore to the south. Founded by Aeolic colonists from Methymna in Lesbos in the 1st millennium bc, the city was constructed on the terraced slopes, partly natural and partly artificial, of an isolated cone of trachyte that rises steeply more than 700 feet (200 m) above the sea. Assus had the only good harbour on the north shore of the Gulf of Adramyti (Gulf of Edremit) and commanded coastal traffic.
Assus came under the rule of the Persians and later of the Athenian empire. It fell to Alexander the Great and subsequently was ruled by the Macedonian general Lysimachus, the kings of Pergamum, and Rome. In response to an invitation from Hermeias of Atarneus, tyrant of Assus, Aristotle founded a Platonic school there (348–345 bc). The Stoic philosopher Cleanthes was born there.
The site was quarried in the 19th century for stone for the docks of Istanbul; nevertheless, much of the old city remains, including the submerged mole of the ancient harbour, parts of the fortifications, and the ruins of a Doric Temple of Athena.